Field Dynamic Test for A Base-Isolated 15-Story Steel Structure

Transcription

1 6 th International Conference on Advances in Experimental Structural Engineering 11 th International Workshop on Advanced Smart Materials and Smart Structures Technology August 1-2, 2015, University of Illinois, Urbana-Champaign, United States Field Dynamic Test for A Base-Isolated 15-Story Steel Structure Y.M. He 1, Y.Q. Yang 2, J.W. DAI 3 1 Postgraduate, Key Laboratory of Earthquake Engineering and Engineering Vibration, Institute of Engineering Mechanics CEA, Harbin, China. yangiem@foxmaill.com 2 Associate Researcher, Key Laboratory of Earthquake Engineering and Engineering Vibration, Institute of Engineering Mechanics, CEA, Harbin, China. yangyongqiang@iem.ac.cn. 3 Researcher, Key Laboratory of Earthquake Engineering and Engineering Vibration, Institute of Engineering Mechanics, CEA, Harbin, China. jwdai@iem.ac.cn. ABSTRACT The paper presented the introduction about the field dynamic test. The tested building was a new constructed base-isolated 15-story steel structure. Ambient vibration tests, free attenuation vibration tests, sinusoidal vibration tests and displacement controlled earthquake simulation tests were carried out respectively. There were more than 70 load cases totally. The acceleration and displacement responses of the structure were measured and recorded as well as the strain responses of critical steel columns and braces. Then, numerical model of this base-isolated 15-story steel structure was established based on the finite element method. According to the natural frequency, equivalent lateral stiffness and damping ratio from the test, the numerical model of the structure was improved. Finally, seismic analyses for the tested structure were also carried out and compared with the test results. This test provides useful reference to the seismic design of base-isolated buildings and finite element analyses. KEYWORDS: field dynamic test, base-isolated, steel structure, free attenuation vibration tests, earthquake simulation test 1. INTRODUCTION In situ test used in geotechnical engineering originally, is mainly refers to field test in the wild area and then gradually extended to field test of buildings. In situ test has the advantage of that it gains the real characteristics and response of the structure under various dynamic loads, avoid the error of the model experiment. But in situ dynamic test of buildings is demanding and cost. So most of researches are still used the model experiment, but not the in situ dynamic test. C.E.Vnetura determined the structure modal, the natural vibration period and damping ratio for a base isolation building by an in situ test in Japan. The finite element model of the base isolation building is established and improved by the experimental data. A field cyclic loading test was carried out by Braga F. for a base isolation building in south Italy. Response of isolation bearings were tested and compared. J.M.W.Brownjohn gained the structure modal of a building through a field test. A frame structure seismic response is obtained by Dai Junwu during an aftershock of Wenchuan earthquake. These in situ tests provide valuable experimental data for researchers.the paper presented a field dynamic test. It s the first time to do the field test for a real base-isolated high-rise building in China. 2. BACKGROUND AND TEST The tested structure is a new constructed office building sitting at Kunming city, Yunnan province of China. The total construction area of the building is about square meters and the total weight is about tons. The building has a total height of 47.4 meters and an aspect ratio of Fourteen layers are on the ground and two layers are underground. The isolation layer is 3.2 meters tall. The ground floor is 4.5 meters high and the rest floors are 3.3 meters high. Plan drawing of the building is shown in figure 1. The base isolation building adopts the Eccentrically-braced steel frames structure system. Eccentric braces were set between two side columns from layer four to layer thirteen, as shown in figure 2.

2 Figure 1 - Plan drawing of the building Figure 2 - Solid drawingof the building Isolation layer is underground and isolation bearings contain laminated rubber bearings (LNR) and lead rubber bearing (LRB). Among them there are three kinds of laminated rubber bearing, is respectively: LNR400, LNR800, LNR900, in which LNR400 bearing for sliding bearing. There two kinds of lead rubber bearing: LRB800 and LRB1000. The arrangement of isolation bearings is shown in figure 3 ant the mechanical properties of the bearings in table 1. The test was carried out by using a 3000 KN hydraulic servo-actuator installed in the basement. The hydraulic servo-actuator is located on the isolation layer and the location is shown as in figure 3. There were more than 70 load cases totally. In all test cases, ambient vibration tests, free damping vibration tests, sinusoidal vibration test and displacement controlled one-dimensional low-level earthquake simulation tests were completed one by one respectively. Limited by the sensor quantity, sensors were arranged around the loading column and the same corner column on every floor for different cases, as shown in figure 3. The acceleration and displacement responses of the structure were measured and recorded deliberately.

3 HYDRAULIC ACTUATOR SENSOR Figure 3 - Arrangement of isolation bearings Table 1 - The mechanical properties of the bearings Vertical Horizontal Beartings Bearing capacity/ kn Stiffness/ kn/mm Shear deformation Stiffness/ kn/mm Damping ratio LRB % % 50% LRB % % LNB % ,4 50% LNR % % LNR NUMERICAL MODEL AND VALIDATION In order to study the dynamic performance of the steel structure building, the numerical model is established by SAP2000 and modified using experimental results in this paper, the model as shown in figure 4. The natural vibration period of the improved numerical model is compared with the measured results are shown in table 2. Figure 4 - Numerical model by SAP2000

4 Displacement (mm) Displacement (mm) Table 2 - Comparision of Simulation and test Vibration mode Simulation/s Test/s By comparing the results of numerical simulation and test, the rationality of the numerical model established is verified in this paper. Two actual earthquake records were selected to carry out the test: strong earthquake records on isolation layer in 2011 East Japan earthquake(gm1) and Xian station ground motion records in 2008 Wenchuan earthquake(gm2), as shown in figure 5. Because the experiment load position is on the isolation layer and GM2 is a record from free field, so, the record cannot be used directly. By the above finite element model, displacement time history curve of the isolation layer can be obtained and used to test load. This test is an earthquake simulation test based on displacement control. There are two cases for each record, PGD for 10mm and 20mm respectively. The acceleration and displacement responses of the structure were measured and recorded during the four cases. Figure 6 and figure 7 show the structural displacement response peak and the acceleration response peak of the test results and simulation results. It can be seen from the diagram that the simulation results are close to the test. The finite element model established in this paper is reasonable Time (s) (a) GM Time (s) (b) GM2 Figure 5 - Time history curve ofdisplacement (a) GM1(PGD=10mm) (b) GM1(PGD=20mm)

5 (c) GM2(PGD=10mm) (d) GM2(PGD=20mm) Figure 6 - the structural displacement response peak (a) GM1(PGD=10mm) (b) GM1(PGD=20mm) (c) GM2(PGD=10mm) (d) GM2(PGD=20mm) Figure 7 - the structural acceleration response peak 4. CONCLUSION This paper mainly introduced the in situ dynamic test, and modified the finite element model of the isolation steel structure using the test results. The finite element model established in this paper is verified by comparing the results of numerical simulation and test. This test provides useful reference to the seismic design of base-isolated buildings and finite element analyses. AKCNOWLEDGEMENT The authors appreciate the financial support from the Earthquake Scientific Research Funds Program (No ) and National Natural Science Foundation of China (No ). REFERENCES 1. Lin Chunyang, Dai Junwu.(2011). In situ text on RC frame lightly damaged by the great Wenchuan earthquake. Structural Engineering, Vol.27 No.s1, Hwang JS, Hsu TY.(2000). Experimental study of isolated building under triaxial ground excitations. ASCE

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